The invention relates to a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles.
In heavy commercial vehicles, the parking brake is actuated by means of what are known as spring force accumulator cylinders (spring-loaded cylinders). Here, the brake actuating force is generated via spring force, with the result that the requirements for a mechanically actuated parking brake are satisfied.
Since the spring force accumulator cylinders are, as a rule, designed to generate very high forces, manual release in the operating case is no longer appropriate. In the case of pneumatically actuated brakes, the parking brake is therefore released by means of compressed air.
In order to make this possible, spring force accumulator cylinders are, as a rule, equipped with a release piston. It is possible by way of this piston, if compressed air is introduced, to compress the spring to such an extent that the brake is released. In order that the parking brake is not engaged while driving, the piston is loaded constantly with compressed air, with the result that the spring cannot be relieved and therefore the parking brake does not start to act.
The most common design is what is known as a combined cylinder. A combined cylinder includes or combines two different brake cylinder types, namely a spring force accumulator cylinder for the parking brake system (PBS) and a compressed air cylinder (usually a diaphragm cylinder) for the service brake system (SBS).
The two cylinders are usually arranged behind one another in an axial direction. The spring force accumulator part which acts with its piston rod on the piston collar of the diaphragm cylinder and by the latter, in turn, on the brake lever, is arranged behind the diaphragm part of the combined cylinder.
This design requires a relatively large amount of installation space. However, the installation space is being limited increasingly by the introduction of more complex chassis systems, such as independent suspension systems, lightweight axles, etc.
There are therefore efforts to minimize the space requirement for the parking brake cylinder by other designs and methods of operation. To this extent, what is known as the compact combined brake cylinder affords a more compact design. DE 10 2005 044 708 A1 (corresponding to U.S. Pat. No. 7,523,999 B2) discloses a brake cylinder of this type, in which the function of the parking brake cylinder is integrated directly into the service brake cylinder. Here, the spring force accumulator spring is no longer actuated via a separate spring force accumulator piston, but rather likewise via the piston of the service brake cylinder.
In order to release the parking brake, the SBS piston is loaded for a short time period by way of a special actuation with compressed air. Since the piston force which is produced here is greater than the maximum compressive force of the accumulator spring, the accumulator spring is compressed. A pneumatically actuated locking mechanism is required to arrest the spring.
This pneumatically actuated mechanism can be implemented in different ways. One option arrests the spring force accumulator spring via a threaded spindle, which is not self-locking. To this end, it is necessary to arrest the threaded spindle by the pneumatically switchable locking mechanism.
The invention has the object of providing the brake cylinder of the generic type with a reliably operating, pneumatically actuable locking mechanism having a compact design.
The invention achieves this object by providing a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles, having a spring force accumulator brake section for carrying out parking brake operations by way of a spring force accumulator spring, and a service brake section for carrying out service brake operations, which are actuated by compressed air. The spring force accumulator brake section and the service brake section are combined in a housing to form one structural unit. The housing is divided by a piston into two spaces, of which one of the two spaces serves as pressure space for actuating the service brake section. The spring force accumulator spring of the spring force accumulator section is arranged in the further space on the opposite side of the piston. The spring force accumulator spring acts in the space on a further spring force accumulator piston, which can be locked with respect to the piston, by way of a pneumatically actuable locking mechanism and can be released from the locking mechanism by release of the latter, and which is connected directly or via further elements to a piston rod for actuating the vehicle brake. After the release of the locking mechanism, the spring force accumulator spring acts between the two pistons and displaces them relative to one another in the case of a parking brake operation. The pneumatically actuable locking mechanism is designed in such a way that it acts only in the expansion direction of the spring.
Advantageous refinements of the invention are described herein.
The invention uses the following effect. During compression of the accumulator spring by the cylinder piston, it is necessary for the threaded spindle to be able to rotate. The threaded spindle therefore must not be blocked by the locking mechanism in this phase.
To this end, a defined functional sequence is necessary during the release of the spring force accumulator brake. The cylinder is controlled here such that the locking mechanism is not loaded with compressed air during the compression of the accumulator spring. The locking mechanism is not activated until the accumulator spring is compressed to the defined dimensions.
However, this functional sequence cannot be guaranteed by way of an external controller in all operating conditions. It is therefore possible according to the invention to compress the accumulator spring by the cylinder piston even when the locking mechanism is activated.
Since the force of the spring always acts in the same direction independently of the movement direction, it is sufficient if the locking mechanism is active only in the expansion direction of the spring.
As a result of the integration of a directionally dependent clutch, the threaded spindle can be rotated only in one direction when the locking mechanism is activated. Here, the freewheel or the ratchet coupling has to be oriented in such a way that the locking action acts in the expansion direction of the accumulator spring.
Reliable arresting of the spring force accumulator spring is important for the function of the compact combined cylinder. In particular, no impairment of the spindle locking should occur as a result of shaking loads and vibrations. A directional clutch, which is based on a positive locking action, therefore appears to be a preferable system for this application.
According to one particularly advantageous variant, the invention is realized in a manner providing a compact and simple design by using a ratchet mechanism integrated into the locking mechanism piston.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.